摘要:

We have applied high-resolution chemical imaging in a transmission electron microscope to study compositional variations across an InGaAs/InAlAs double quantum well structure in the (100) orientation. The structures of interest are grown on an InP support and consist of two 40 Å layers of InGaAs separated by 20 Å of InAlAs. For this(InGa)x(InAl)1−xAssystem, we have obtained compositional information with an accuracy of about 20&percent; and a maximum spatial resolution of1/4unit cell. The results clearly show compositional irregularities on a monatomic scale. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119698

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A nonlinear effect in the electrodynamics of hard superconductors is predicted and theoretically studied. It is shown, that a low-frequency (LF) electromagnetic wave can pass through a superconducting plate, due to its interaction with another wave propagating in the opposite direction, even at small amplitudes of the LF wave when it cannot reach the opposite boundary of the sample without assistance. The dependence of the LF surface impedance on the amplitude of the high-frequency (hf) wave is studied within the framework of the critical state model. The LF surface impedance is found to be drastically increased by the overlapping of the regions of wave penetration. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119699

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The coupling effects of a commercial dc superconducting quantum interference device (SQUID) to an electricalLCresonator which operates at audio frequencies(≈1 kHz)with quality factorsQ≈106are presented. The variations of the resonance frequency of the resonator as functions of the flux applied to the SQUID are due to the SQUID dynamic inductance in good agreement with the predictions of a model. The variations of the quality factor point to a feedback mechanism between the output of the SQUID and the input circuit. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119700

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this letter we show thatSrCuO2/BaCuO2andCaCuO2/BaCuO2based artificial structures of very good crystallographic quality can be grown by pulsed laser deposition. We demonstrate that the most important parameters which determine the superconductive properties are the chemical composition, the oxygen growth pressure, and theCO2contamination. A major difference is found in the behavior of resistivity between films containing Sr and Ca, respectively. Namely [BaCuO2]2/[SrCuO2]nfilms never show any trace of superconductivity, while [BaCuO2]2/[CaCuO2]nfilms result in having, for growth oxygen pressuresPO2⩾0.2 mbar, a full transition withTc(zero resistance) up to 46 K. Furthermore we demonstrate that even a tiny amount ofCO2in the oxygen growth atmosphere can suppress completely the superconducting properties of these artificial structures. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119923

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Optimized sputteredYBa2Cu3O7(YBCO) thin films onCeO2-buffered sapphire substrates are patterned into square lattices of submicrometer holes (antidots) with diameters of 250–450 nm and lattice parameters ofd=500–1000 nmwithout deterioration of superconducting properties. In the mixed state, matching effects between the Abrikosov vortex lattice and the artificial antidot lattice are observed. These effects are in the form of peaks or cusps in the critical current density recorded as a function of magnetic induction at integersnand specific rationalsk/lof the matching fieldBm=(&Fgr;0/d2).The experimental results are discussed in the context of existing theories. The existence of multiquanta vortices confined by the holes in YBCO films are considered. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119701

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A complete magneto-optical characterization of any material requires the measurement of both, the magneto-optical and the conventional optical constants. We have developed the method of generalized magneto-optical ellipsometry (GME), which enables us to determine these material constants simultaneously in a single setup. In addition, GME even allows the determination of the magnetization orientation. The experimental setup is very simple, using only two rotatable polarizers as polarization sensitive elements. Our experimental results for permalloy demonstrate the validity of our approach and the feasibility of GME as a practical measurement technique. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119669

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Epitaxial ferromagnetic manganite films have been sputtered on bicrystal substrates. Their magnetoresistance was measured as a function of magnetic field and temperature. The grain boundary magnetoresistance at low temperature is separated from the intrinsic magnetoresistance near the Curie temperature. The grain boundary magnetoresistance peaks at about 100 Oe and saturates at about 2 kOe. For aLa0.8Sr0.2MnO3film with a grain boundary angle&thgr;=36.8°a field independent componentr0=4.1×10−6 &OHgr; cm2was separated from a field-dependent component which has its maximumrH=2.3×10−6 &OHgr; cm2forHof order the coercive field. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119702

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A correlation is found between the sign of the magnetoresistance&Dgr;R=(RP−RAP)and the sign of the interlayer coupling in MnGa/(Mn,Ga,As)/MnGa trilayers (subscript P,AP=parallel,antiparallel magnetic alignment of both MnGa layers). Ferromagnetic coupling results in&Dgr;R<0,antiferromagnetic coupling results in&Dgr;R>0.This correlation has not been observed before and can not be explained by the usual model for giant magnetoresistance in magnetic multilayers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119703

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel magnetoelectronic device incorporating a single microstructured ferromagnetic film and a micron scale Hall cross was fabricated and characterized at room temperature. Magnetic fringe fields from the edge of the ferromagnet generate a Hall voltage in a thin film semiconducting Hall bar. The sign of the fringe field, as well as the sign of the output Hall voltage, is switched by reversing the magnetization of the ferromagnet. This new device has excellent output characteristics and scaling properties, and may find application as a magnetic field sensor, nonvolatile storage cell, or logic gate. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119704

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thin films of perovskite manganiteLa0.7Ca0.3MnO3were grown epitaxially onSrTiO3(100), MgO(100) andLaAlO3(100) substrates by the pulsed laser deposition method. Microscopic structures of these thin film samples as well as a bulk sample were fully determined by x-ray diffraction measurements. The unit cells of the three films have different shapes, i.e., contracted tetragonal, cubic, and elongated tetragonal forSrTiO3,MgO, andLaAlO3,respectively, while the unit cell of the bulk is cubic. It is found that the samples with a cubic unit cell show smaller peak magnetoresistance at low fields(≲1 T)than the noncubic ones do. The present result demonstrates that the magnetoresistance ofLa0.7Ca0.3MnO3at low fields can be controlled by lattice distortion via externally imposed strains. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119705

出版商:AIP    

年代:1997

数据来源: AIP